1. Field of this invention
This invention relates to a fastener system and relates particularly to a recessed screw, a punch for forming a socket on a screw head and a driving tool for use in the screw head.
2. Description of the Related Art
International universal recesses of screw heads for engaging with driving tools, as shown in FIG. 1, may include “slotted” sockets, “Phillips” sockets, “Pozi” sockets, square sockets, hexagonal sockets, “Torx” sockets and so on. Generally, the driving tools and the screws with corresponding sockets are usually made by different manufacturers, so the driving tools are usually unable to be completely received in the sockets of the screw heads. If the driving tool is given a higher driving torque, the socket may become deformed when it cannot bear the torque, or the driving tool may slip out of the socket because of the torque that the screw head cannot undertake. These problems decrease the driving efficiency, render the socket unable to be used because of the deformation, affect the duration of the screw and cause the incompleteness of the screwing process. Accordingly, some manufacturers have invented screws with special drive sockets to enhance the engagement between the socket and the tool. Those screws can only cooperate with their corresponding tools, but they cannot receive tools adapted to the international universal sockets as described above. Thus, those special sockets cannot be widely used in the global market.